1. Field of the Invention
The present invention relates to a method and apparatus for assessing the neural integrity of a patient""s central nervous system.
2. Brief Description of the Prior Art
It is well known to those of ordinary skill in the art that""stimulating an eye with flickering light induces strong neural activity resulting in oxygen consumption of the human brain [Thomas, C. G.; Menon, R. S.; (1998); xe2x80x9cAmplitude Response and Stimulus Presentation Frequency Response of Human Primary Visual Cortex Using BOLD EPI at 4 Txe2x80x9d; Magnetic Resonance Medicine, 40, 203-209] and the optic nerve head of the cat [Ahmed J.; Linsenmeier, R. A.; Dunn, R. Jr.; (1994); xe2x80x9cThe Oxygen Distribution in the Prelaminar Optic Nerve Head of the Catxe2x80x9d; Experimental Eye Research, 59, 457-465]. It is also known from the literature that selective adaptation or stimulation of one eye will induce sensitivity changes in the other, contralateral eye; this phenomenon is called xe2x80x9cinterocular transferxe2x80x9d [Andrews T. J.; White, L. E.; Binder, D,;Purves, D.; (1996); xe2x80x9cTemporal Events in Cyclopean Visionxe2x80x9d; Proceedings of the National Academy of Sciences USA, 93, 3689-3692]. These studies imply the role of central mechanisms, e.g. the human brain, as being responsible for the control of the sensitivity changes observed in the contralateral eye. It is also reported that cerebral infarcts will induce oxygen changes measured at the level of the contralateral eye [Staedt, U.; Hutt M.; Herrmann B.; Seufzer, U.; Leweling H.; (1989); xe2x80x9cEffect of Hemoglobin with 10% Hydroxyethyl Starch Solution (MW 200,000/9.5) on the Flow Properties of Blood, Arterial Blood Gases and Conjunctival Oxygen Partial Pressure in Patients with Cerebral Infarctxe2x80x9d; Infusionstherapie, 16, 107-112].
Epilepsy, migraines with visual auras, and temporary amnesia have all been associated with cortical depression spreading (CD) in the brain, as reported in the following articles:
[Dahlem, M. A.; Engelmann, R.; Lowel, S.; Muller, S. C.; (2000); xe2x80x9cDoes the Migraine Aura Reflect Cortical Organization?; Eur J Neurosci, 12, 767-770];
[Donnet A.; Bartolomei, F.; (1997); xe2x80x9cMigraine with Visual Aura and Photosensitive Epileptic Seizuresxe2x80x9d; Epilepsia, 38, 1032-1034];
[Kager, H.; Wadman, W. J.; Somjen, G. G.; (2000); xe2x80x9cSimulated Seizures and Spreading Depression in a Neuron Model Incorporating Interstitial Space and Ion Concentrationxe2x80x9d; J Neurophysiol., 84, 495-512];
[Kaube, H.; Herzog, J.; Kaufer, T.; Dichgans, M.; Diener, H. C.; (2000); xe2x80x9cAura in Some Patients with Familial Hemiplegic Migraine can be Stopped by Intranasal Ketaminexe2x80x9d; Neurology, 55, 139-141];
[Pantoni, L.; Lamassa, M.; Inzitari, D.; (2000); xe2x80x9cTransient Global Amnesia; A Review Emphasizing Pathogenic Aspectsxe2x80x9d; Acta Neurol Scand., 102, 275-283]; and
[Sotak, C. H.; (1999); xe2x80x9cNew NMR Measurements in Epilepsy. Diffusion-Weighted Magnetic Resonance Imaging of Spreading Depressionxe2x80x9d; Adv Neurol, 79, 925-929].
Cortical depression spreading can be induced by stimulation and results in a widespread decrease in oxygenation of the brain followed by a change in neural potentials.
An object of the present invention is to assess the neural integrity of the central nervous system of a patient by stimulating the patient with a visual or auditory flickering stimulus and detecting oxygenation changes in at least one eye of the patient.
More specifically, in accordance with the present invention, there is provided a method for assessing neural integrity of a patient""s central nervous system, comprising stimulating the patient with a visual or auditory flickering stimulus, sensing oxygenation in at least one eye of the patient, and detecting whether a change in the sensed oxygenation occurs in response to stimulation of the patient with the flickering stimulus. This change is indicative of neural integrity of the patient""s central nervous system.
Also in accordance with the present invention, there is provided an apparatus for assessing neural integrity of a patient""s central nervous system, comprising a generator of a visual or auditory flickering stimulus, and a neural integrity assessment instrument responsive to oxygenation in at least one eye of the patient. The flickering stimulus is applied to the patient to stimulate this patient, and the neural integrity assessment instrument comprises:
a sensor of oxygenation in at least one eye of the patient; and
a detector of a change in the level of the sensed oxygenation in response to stimulation of said patient with the flickering stimulus, this change being indicative of neural integrity of the patient""s central nervous system.
The present invention further relates to method for assessing neural integrity of a patient""s central nervous system, comprising stimulating a first eye of the patient with a flickering light, sensing oxygenation in the patient""s second eye, and detecting whether a change in the sensed oxygenation occurs in response to stimulation of the patient""s first eye with flickering light, this change being indicative of neural integrity of the patient""s central nervous system.
In accordance with preferred embodiments of this method:
sensing oxygenation in the patient""s second eye comprises sensing levels of oxygenation at the optic nerve head of the fundus of the patient""s second eye; and
stimulating the patient""s first eye comprises adjusting at least one of the following parameters to generate at least one desired neural response of the patient""s central nervous system: an intensity of the flickering light, a contrast of the flickering light, a color of the flickering light, a flicker rate of the flickering light, and a duration of the stimulation of the patient""s first eye with flickering light.
The present invention still further relates to an apparatus for assessing neural integrity of a patient""s central nervous system, comprising a generator of flickering light applied to a first eye of the patient to stimulate this patient""s first eye, and a neural integrity assessment instrument responsive to oxygenation in the patient""s second eye. The neural integrity assessment instrument comprising:
a sensor of oxygenation in the patient""s second eye; and
a detector of a change in the level of the sensed oxygenation in response to stimulation of the patient""s first eye with flickering light, this change being indicative of neural integrity of the patient""s central nervous system.
According to preferred embodiments of this apparatus:
the sensor is positioned to sense levels of oxygenation at the optic nerve head of the fundus of the patient""s second eye;
the generator comprises a source of light operated through a flickering-light controller, the source of light is selected from the group consisting of a light-emitting diode and a laser, and a fiber optic cable is interposed between the source of light and the patient""s first eye to guide light from the source of light to the patient""s first eye; and
the neural integrity assessment instrument comprises an on-line oxygenation measurement device.
Still further in accordance with the present invention, there is provided a method for assessing neural integrity of a patient""s central nervous system, comprising stimulating at least one ear of the patient with an auditory flickering stimulus, sensing oxygenation in at least one eye of the patient, and detecting whether a change in the sensed oxygenation occurs in response to stimulation of the patient""s at least one ear with the auditory flickering stimulus, this change being indicative of neural integrity of the patient""s central nervous system.
According to a preferred embodiment, stimulating the patient""s at least one ear comprises adjusting at least one of the following parameters to generate at least one desired neural response of the patient""s central nervous system: an amplitude of the auditory flickering stimulus, a frequency of the auditory flickering stimulus, a pitch domain of the auditory flickering stimulus, a flicker rate of the auditory flickering stimulus, and a duration of the stimulation of the patient""s at least one ear with the auditory flickering stimulus.
Again in accordance with the present invention, there is provided an apparatus for assessing neural integrity of a patient""s central nervous system, comprising:
a generator of an auditory flickering stimulus, this auditory flickering stimulus being applied to at least one ear of the patient to stimulate this patient""s at least one ear;
a neural integrity assessment instrument responsive to oxygenation in at least one eye of the patient, this neural integrity assessment instrument comprising:
a sensor of oxygenation in the patient""s at least one eye; and
a detector of a change in the level of the sensed oxygenation in response to stimulation of the patient""s at least one ear with the auditory flickering stimulus, this change being indicative of neural integrity of the patient""s central nervous system.
According to a preferred embodiment of this apparatus, the generator comprises a source of auditory flickering stimulus connected to an earphone.